1. Field of the Invention
This invention relates to a fuel injection control system for internal combustion engines, and more particularly to a fuel injection control system of this kind which controls the amount of fuel injection in dependence on the amount of fuel adhering to the wall surface of the intake pipe of the engine.
2. Prior Art
There have already been proposed by the present assignee a fuel injection control system for internal combustion engines which carries out so-called adhering fuel-dependent correction of the fuel injection amount in dependence on the amount of fuel adhering to the wall surface of the intake pipe of the engine, in which the fuel injection timing is controlled such that the ratio of the amount of fuel injected and directly drawn into the combustion chamber to the whole amount of fuel injected, i.e. the direct supply ratio, becomes the maximum (Japanese Patent Application No. 6-13999), and a fuel injection control system of the same kind, in which during starting (cranking) of the engine, sequential fuel injection is carried out from the very outset of fuel injection instead of carrying out simultaneous fuel injection, while the adhering fuel-dependent correction is simultaneously carried out for correction of the amount of fuel injection during the starting of the engine (Japanese Patent Application No. 6-36467).
Further, a fuel injection control system has been proposed by Japanese Laid-Open Patent Publication (Kokai) No. 3-130546, which detects the volatility (heaviness) of fuel used in an internal combustion engine to carry out the adhering fuel-dependent correction of the fuel injection amount according to the detected volatility of fuel.
However, the fuel injection control system proposed by the present assignee has the following inconvenience: When the engine is started immediately after being refueled with a fresh fuel which is different in volatility from the older fuel which has been used, an air-fuel ratio sensor of the engine has not been activated yet so that it is impossible to carry out the air-fuel ratio-dependent correction of the fuel injection amount, and values of adhering fuel-dependent correction parameters which have so far applied for the adhering fuel-dependent correction, become unsuitable for the fresh fuel. As a result, the fuel supply amount becomes insufficient, causing engine stalling in the worst case.
Further, according to the fuel injection control system proposed by Japanese Laid-Open Patent Publication (Kokai) No. 3-130546, it takes much time to detect the volatility of the fuel, which makes it impossible to carry out the adhering fuel-dependent correction according to the volatility of the fuel, during or immediately after the start of the engine. Therefore, the system can suffer from similar unfavorable results to those described above.